One issue I frequently address is when the digital transfer substrate imprints a permanent line onto the garment. This happens because the heat needed to transfer items onto polyester and the accompanying pressure actually makes the polyester melt, and it conforms to the edge of the transfer carrier.
The way to eliminate this is through a little bit of trial and error, but there are a few key points to help narrow down a solution. The first and easiest way to eliminate this is to make the transfer carrier (paper, vinyl carrier sheet, mask, etc.) larger than the heat press itself.
Another, better way to eliminate this mark is by using a piece of high temperature foam. Cut the foam to at least 1/2” smaller than the transfer carrier sheet, but make sure it is bigger than the image area being transferred. Before pressing, stick the foam into your heat press, toward the edge, so you can see it. Adjust the pressure on your heat press so the foam compacts to about half of its normal thickness. This will provide a good amount of pressure without pushing down so hard that you imprint the transfer carrier’s edge.
—Aaron Montgomery, Coastal Business Supplies